Flotation is a process for concentrating minerals, or other valuable constituents, from their ores. In an ore flotation process the ore is crushed or wet ground to obtain a water slurry or pulp. Additives such as flotation or collecting agents and frothing agents are added to the pulp to assist in subsequent flotation steps in separating the valuable constituents from their ores. The flotation or collecting agents can comprise solid material and/or liquids such as oils, other organic compounds, or aqueous solutions.
Mineral flotation is accomplished by aerating the pulp, so that mineralized bubbles rise to the surface of the flotation cell producing a layer of froth which contains and supports pulverized mineral. The froth is then scraped or permitted to flow over the lip of the cell to effect the separation. The thus concentrated mineral bearing froth is collected and further processed to improve the concentration of desired minerals. The pulp may be further processed to recover other valuable minerals.
The equipment most commonly used in a flotation plant comprises equipment for crushing, grinding, size classification and flotation. Since the flotation residence time may vary widely, depending on the particular separation, it is usually necessary to use many flotation cells in series to allow sufficient time for all the valuable mineral to float. For example, units of 12-18 individual flotation cells are commonly used in series for copper sulfide flotation.
The froth flotation process requires the presence of a stable froth layer above the pulp for recovery of concentrated minerals. Such froth layers are generated by the use of additives known as frothers. Many designs of flotation cells, which are suitable for generating a froth layer for skimming, have been used at different times during the past 60 years. In any flotation cell, however, both pulp and froth levels are important operating variables for achieving optimum performance.
Liquid level measurement in atmospheric vessels, such as pulp level in a flotation cell, rarely presents any serious problems. Instrumentation generally can be selected and installed so that it can be removed from the vessel for calibration or repair without draining the vessel. On the other hand, various measurement techniques, such as capacitance probes, impedance probes, optical sensors and ultrasonic detectors, are known for froth or foam level measurement. None of these froth level measurement techniques, however, have proven to provide satisfactory results for level measurement of froth, which contains pulverized minerals. In particular ultrasonic level detectors, which measure the time required for an ultrasonic pulse to travel to a surface and back, are ineffective for ore flotation cells because the froth does not provide a suitable reflective surface for the ultrasonic pulses.
In view of the difficulty in measuring froth level, it is fairly common for commercial flotation plants to measure the pulp level in a flotation cell and assume that the froth level is a fixed distance above the lip of the flotation cell. While this inferred determination of froth level, based solely on pulp level, can provide satisfactory results under certain steady state conditions, it is unsatisfactory during transient conditions when any of the numerous operating variables, which may affect froth level, are changed. For example, a change in the rate of adding the frothing agent will cause a corresponding change in the froth level which cannot be inferred from the pulp level.
Accordingly, it is an object of this invention to provide method and apparatus for accurately measuring froth level in an ore flotation cell.
It is a further object of this invention to provide a wire guided float level measurement device which is suitable for use for froth level measurement in an ore flotation cell.
Another object of the invention is to provide apparatus for measuring the froth level in a flotation cell which is simple, fast, and economical.
Still another object of this invention is to improve the control of a froth layer of desired thickness for the optimum recovery of the concentrated mineral.